Projectiles fired from barrels follow trajectories that are well-defined or predictable. In use, a firing control or ballistic computer determines the barrel's angle of inclination a for a specific projectile type when given a desired impact point, barrel conditions, wind velocity, etc. However, due to variations in the amount of explosive charge primed in a cartridge of each projectile, tolerances in the driving band and associated barrel wear and thermal expansion, cleanliness of the barrel, variations in humidity, and so on, the muzzle velocity of each projectile after exiting from the barrel suffers some deviations. The deviations in the muzzle velocity thus cause the impact point to deviate from the desired target position. In addition, after a projectile is air-borne, variations in wind velocity and environmental factors also affect the accuracy of the impact or detonation position.
For large projectiles, there may be sufficient space and payload to employ active tracking of the target position. Target tracking may use global position system, laser, etc., and supplementary booster and/or steering fins and brakes. However, for small and inexpensive projectiles, target tracking is not employed; for example, U.S. Pat. No. 7,021,187, assigned to the US army, describes an ammunition launcher in which trigger time of a typical ammunition is permanently programmed into a fuse contained therein. Deviations in muzzle velocity and variations in environmental factors cannot be accounted for in setting the trigger time of the ammunition.
A known method for updating the trigger time of a small projectile is to track the speed of each projectile, for example, by Doppler or laser tachometer and re-programming the trigger time according to the remaining flight time to the target position; for example, U.S. Pat. No. 6,216,595, assigned to Giat Industries, describes such a method. Thus, there is a need for other methods of tracking or determining the speeds of small projectiles so that the trigger time of each projectile can be programmed or updated to optimize the effect of the projectile.